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Spencer R.
Stanford Student, Tutor for 6 years
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Chemistry
TutorMe
Question:

Explain how to electroplate a copper penny (E˚cell = +0.34V) with zinc metal (E˚cell = -0.76). Your main apparatus is as follows: a battery with a positive and negative terminal, a beaker with zinc nitrate Zn(NO3)2 solution, one copper electrode and one copper penny. Explain the processes occurring. What type of cell is this? Voltaic or electrolytic? What must be the minimum voltage of the battery?

Spencer R.
Answer:

An electrolytic cell will be needed to electroplate the penny. Electrolytic cells involve using an electric current to drive reactions in the non-spontaneous direction. Zinc has a lower cell reduction potential than copper so if zinc is reduced and copper oxidized, electrons will be flowing from an area of lower potential energy to higher potential energy and the reaction will be non-spontaneous. The overall standard cell electrode potential will be: Formula: E˚cell = E˚cell (cathode) - E˚cell (anode) So.... E cell = -0.76V(cathode, zinc reduced) - 0.34V (anode, copper oxidized) = -1.10V The overall cell potential of this electrolytic cell is negative - another indicator that the reaction is non-spontaneous. To drive the reaction in this direction (non-spontaneous) the battery must at least have a voltage of 1.10V. As in all redox reactions, reduction will take place at the cathode and oxidation at the anode. In an electrolytic cell the cathode is the negative end and the anode is the positive end. Thus the copper penny will be connected to the negative terminal and the copper electrode, the positive terminal. At the anode, copper will be oxidized so the copper atoms in the electrode will go into solution. Cu(s) --> Cu2+(aq) +2e . Since copper cations are blue a blue solution will be visible around the copper anode. At the cathode, zinc will be reduced so the zinc ions in solution will form a black solid on the copper penny. Zn2+ (aq) + 2e --> Zn(s).

Literature
TutorMe
Question:

How is the theme of nature used to express character identity in the poem "Where I Come From" (below)? Where I Come From -Elizabeth Brewster People are made of places. They carry with them hints of jungles or mountains, a tropic grace or the cool eyes of sea-gazers. Atmosphere of cities how different drops from them, like the smell of smog or the almost-not-smell of tulips in the spring, nature tidily plotted in little squares with a fountain in the centre; museum smell, art also tidily plotted with a guidebook; or the smell of work, glue factories maybe, chromium-plated offices; smell of subways crowded at rush hours. Where I come from, people carry woods in their minds, acres of pine woods; blueberry patches in the burned-out bush; wooden farmhouses, old, in need of paint, with yards where hens and chickens circle about, clucking aimlessly; battered schoolhouses behind which violets grow. Spring and winter are the mind’s chief seasons: ice and the breaking of ice. A door in the mind blows open, and there blows a frosty wind from fields of snow.

Spencer R.
Answer:

Expressed in the first line of the poem: “People are made of places”, the narrator in Elizabeth Brewster’s “Where I Come From” is a product of her environment. In this poem, the “place” the narrator is from is the natural, rustic, Canadian countryside. By juxtaposing the dull, unsavory aesthetics of the city with the refreshing and inspiring imagery of the countryside Brewster conveys to readers how central nature is to the narrator's identity. Brewster uses the theme of nature to expose what she perceives as undesirable aspects of the city. Experiencing her childhood in a rural lumber town, Brewster is passionate about her countryside origins. This affection towards the countryside is evident as her speaker describes examples of places people “carry” with them as: “hints of jungles or mountains” and “cool eyes of sea-gazers”. These romantic images of picturesque topography and stunning seascapes imply that Brewster’s speaker believes the best places for people to experience are natural. Therefore, the resulting juxtaposition, when Brewster elaborates on experience of the artificial city, has a depressing effect. Firstly, the “smell of smog”, suggests that city air is repulsive. Particularly, the sibilance of the “s” sound emphasizes both the lingering of the foul scent and dismal drone of city life. Secondly the “almost-not-smell” of tulips in the spring mentioned, is a harsh criticism of the city’s treatment of nature. The phrase “almost-not” demonstrates her recognition of the lacking invigorating smell. She echoes this skepticism with the description of “nature tidily plotted in little squares”. Although the adjective “tidily” seems to be a compliment, the “squares” have a limiting effect on nature. Even more infuriating, is the use of enjambment in the lines: “Atmosphere of cities/ how different drops from them”. The line break destroys the grammatical structure of the sentence which makes it cumbersome and uncomfortable to read. This perhaps mirrors the narrators discomfort and difficulty adjusting to city life. The finish of this troublesome clause with the pronoun “them” underlines her hate of the city, and that doesn’t consider herself a part of it. Instead, Brewster’s speaker has an emotional connection to the “acres of pine woods” and Canada’s wilderness. Brewster creates a physical separation between the city and her home by using double indentation. The “acres” of woods contrast with the crowded city and imply that the countryside is open—limitless. The hyperbole the speaker uses: “people carry woods in their minds” suggests that where the speaker comes from -- the forest inspires awe through its beauty. The mention of “blueberry patches” in the brush, contrasts with the precise, “squares” in which plants grow in the city. Blueberries are tasty and enjoyable, and the contrast highlights the superiority of unfettered natural growth in the country. In addition to natural freedom, the narrator explains free and unpressured way of living in the county: “Spring and winter/ are the mind’s chief seasons”. This is an observation that country people measure, and think about life as a long, continuous, slow process. This contrasts with the phenomenon of "rush hours" in the city and the hectic daily schedule which puts people (including the narrator) on edge. Contemplating the alternative, more calm way of life in the countryside sparks the speaker’s nostalgia for home. The line break between stanzas two and three, indicates the moment when the speaker pauses and recounts these past moments. The statement “a door in the mind blows open” suggests that it is a wind—a natural force that has opened her mind. This “frosty” wind from “fields of snow” is perhaps an image from her childhood. This narrator longs to return to the original, unadulterated way of life in her hometown. For Brewster’s character nature is a means for her to compare two differing types of life: in the city and the country. The sensory experience she has allows her to criticize urban life and praise rural life. However, ultimately nature is connected to the narrator's nostalgic longing for her hometown.

Biology
TutorMe
Question:

With reference to genetic inheritance and sex chromosomes, explain why men are more likely to be red-green color blind than women.

Spencer R.
Answer:

Red-green colorblindness is a sex-linked trait. A sex-linked trait whose gene has its locus on either the X or Y chromosome. The gene for the color blindness trait is carried on the X chromosome. There are two alleles: dominant and recessive. Females have two X chromosomes whereas males have one X chromosome and one Y chromosome. Since males only have one X chromosome (inherited from their mother), males can have the red-green color blindness phenotype by inheriting just a single recessive color blindness allele from their mother. Males can be colorblind If their mother is either homozygous recessive (two recessive alleles) or is a carrier (one recessive, one dominant allele) for the red-green colorblindness gene. In contrast, since females have two X chromosomes they can only have the red-green colorblindness phenotype if they inherit two recessive alleles. That means they must inherit a recessive allele from both their mother and father. This is far less likely than just inheriting a recessive allele from their mother. Thus males are more likely to be red-green color blind than women.

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